Starter Cultures for Food Applications
Starter Cultures for food applications are microbial preparations containing at least one microorganism at a high cell concentration, which, when added to raw materials, control and accelerate the fermentation process in food production. The primary strains are derived from lactic acid bacteria, yeasts, and molds, and they perform functions such as acid production, flavor compound generation, protein hydrolysis, and the synthesis of bioactive substances, making them crucial in fermented food manufacturing.
Fermentation/Probiotic Properties
* Genetic stability
* Fermentation rate, post-acidification
* Flavor
* Texture
* Health benefits
Production Performance
* Production conditions, process
* Production efficiency
* Freeze tolerance
* Drought tolerance
Stability
* Storage condition limitations
* Moisture content, water activity
* Survival rate
* Fermentation performance
Yogurt Starter Cultures
Yogurt starter cultureslike Yogurt Starter Culture Yo-ZC912, Yogurt Starter Culture Yo-ZC458, and Yogurt Starter Culture Yo-ZC272 are characterized by their ability to produce acid and aroma. When selecting them, factors such as strain viability, stability, acidification rate, and post-acidification must be considered. Commonly used strains include *Streptococcus thermophilus* and *LactoBacillus delbrueckii* subsp. *bulgaricus*. Ensuring the quality of the raw milk and the inoculation level of the starter culture is important. The fermentation process should be controlled at a temperature of 40-45°C for 3-10 hours. Set-style yogurt requires static fermentation, while stirred yogurt needs agitation after fermentation. Flavor yogurts also require the addition of fruits and vegetables, and fermentation conditions may vary. An appropriate yogurt starter culture can result in a rich mouthfeel and a balanced sweet-sour taste. The ratio of different strains influences acidity, viscosity, aroma, and overall sensory profile. The mainstream combination is LB (*Lactobacillus bulgaricus*) and ST (*Streptococcus thermophilus*), which can be co-cultured with other strains like *Bifidobacterium* or *Lactobacillus plantarum* as needed.
Screening of Yogurt Starter Culture Strains
Employing strains with high fermentation activity can shorten yogurt fermentation time, reduce the risk of contamination, improve production efficiency, lower production costs, and enhance a company's economic returns. Screening strains from spontaneously fermented milk is characterized by randomness and chance, lacking specific indicators during the screening process, and incurs higher screening costs. Strain screening through adaptive domestication involves placing strains in suboptimal environments and subculturing them over generations to gradually acclimate them to these conditions, building tolerance, thereby enabling continuous growth and reproduction in unfavorable environments. Strain screening via Prt S protease, a serine protease belonging to the *Bacillus subtilis* protease family, involves degrading proteins to provide peptides and free amino acids for strain growth, possessing the potential to promote strain proliferation. Assessment on a modified Fructose-Glycerol-Phosphate-Agar (FSDA) medium indicates protease activity if colonies are large, white or pale yellow, translucent, and circular.
Flavor is a significant factor influencing yogurt quality and consumer preference. Screening strains that are high producers of diacetyl, typically generated by *Lactococcus lactis* subsp. *lactis*, can impart a buttery aroma to yogurt; even at very low concentrations (2 μg/mL), it contributes a distinctive creamy flavor. Screening strains that are high producers of acetaldehyde is also important, as high-quality yogurt should contain at least 8 μg/mL of acetaldehyde to provide a desirable aromatic flavor. Screening strains with high proteolytic activity aids lactic acid bacteria by hydrolyzing proteins, providing essential amino acids and releasing peptides that can act as receptors for flavor compound reactions, thereby enhancing yogurt's flavor and nutritional value. Changes in yogurt flavor, primarily an intensified sourness, can negatively impact consumer palatability and reduce product shelf life.